The epidermis is the outermost layer of the skin and forms the protective wrap over the body's surface. The epidermis can be further subdivided into strata with the outermost layer of the epidermis being the stratum corneum which is responsible for keeping water in the body and keeping harmful chemicals and pathogens out, making skin a natural barrier to infection. Transepidermal water loss, i.e., water that passes from inside a body (animal or plant) through the epidermal layer (skin) to the surrounding atmosphere via diffusion and evaporation processes, is a normal part of the cellular activity and regulated by the stratum corneum. Excessive transepidermal water loss, however, activates an inflammatory response in the epidermis and the dermis.
Corneotherapy is a skin care concept based on repairing the stratum corneum and therefore improving the function of the skin barrier. Topically applied substances influence the biochemistry in the horny layer of the skin and subsequent processes in deeper skin layers, which consequently have effects on the constitution of the horny layer, creating a cyclical effect that starts at the surface of the skin. A healthy and functioning skin barrier provides overall protection against dehydration and the penetration of germs, allergens, irritants, radicals, and radiation. This protection supports a gradual reduction in inflammation and other skin problems as the external causative agents are repelled by an intact skin barrier.
Wound healing, or wound repair, is a process in which the skin repairs itself after injury. In normal skin, the epidermis (outermost layer) and dermis (inner or deeper layer) exists in a steady-stated equilibrium, forming a protective barrier against the external environment. Once the protective barrier is broken, the normal (physiologic) process of wound healing is immediately set in motion.
The wound healing process is susceptible to interruption or failure leading to the formation of chronic non-healing wounds, that is, a wound that does not heal in an orderly manner and in a predictable amount of time as compared to wounds resulting from surgery (also sometimes known as wounds of primary intention) or wounds caused by trauma; for example, wounds that do not heal within several months are often considered chronic. Chronic wounds present a particularly difficult problem to treat and are typically classified into three categories: venous ulcers, diabetic, and pressure ulcers. A small number of wounds that do not fall into these categories may be due to causes such as radiation poisoning or ischemia. Chronic wounds, especially ulcerative wounds such as pressure ulcers (bed sores), diabetic ulcers, venous ulcers, etc. that, without treatment, are often trapped in the inflammation phase of wound healing. These types of wounds often accelerate quickly and damage not only the skin, but underlying tissues as well. The excessive healing time required for these types of wounds can lead to secondary complications, such as permanent underlying tissue damage, nerve damage, loss of circulation, and even mortality.
Pressure ulcers and certain other chronic wounds are sometimes categorized according to severity by the use of stages. According to one protocol, Stage I is characterized by a surface reddening of the skin; to the unaided eye, the skin is unbroken and the wound is superficial. Stage II is characterized by a partial thickness skin loss involving the dermis and/or epidermis, typically presenting as an abrasion, blister (broken or unbroken), shallow crater or other lesion, that is visible to the unaided eye. Stage III wounds extend through all of the layers of the skin and are a primary site for a serious infection to occur. Stage IV wounds extend through the skin and involves underlying muscle, tendons and bone. The term “peripheral to the wound” or “peri-wound area” refers to the area adjacent to a wound (a Stage II, III or IV wound) and typically extends from immediately adjacent the wound up to about 3 to 5 cm.
There are two distinct mechanisms for cell death. Apoptosis is the result of “normal” or programmed cell death. Through this physiological process cells are routinely eliminated, giving balance to the proliferation of new cells. During apoptosis the outer membrane of the cell forms “bubbles” known as blebs. The content of the cells becomes incased in the blebs. The blebs separate from the cell and are digested by nearby cells or macrophages. This orderly process greatly reduces toxicity to surrounding cells.
Necrosis is the other form of cell death. This is not a programmed event and is known as “accidental” death. This pathological process occurs when cells are exposed to extreme stress, chemical insult, and resultant free radical damage. The early stages of necrosis involve a swelling of the cell called oncosis. During oncosis the cell and its organelles begin to swell due to an exchange in the cell's potassium to sodium ratios. Necrosis, after the oncosis stage, is an explosive event where the cells contents stream directly into the surrounding cells environment causing damage and an immune response. Controlling necrosis during the early oncosis stage is important. Up to this point, necrosis is a reversible event. The morphology of cells dying by necrosis centers on changes in the cell's permeability. Hengartner M O, The biochemistry of apoptosis. Nature 407:770-776, 2000. Osmotic changes take place during an exchange of cytosol potassium and extracellular sodium. Early stage necrosis, known as oncosis, is characterized by the dilation or swelling of the cell and its organelles due to this exchange. Cell survival of this non-programmed event is dependent upon repairing the cell's membrane and stopping the flow of sodium ions into the cells interior. Repair of the cell's membrane and improvement in the cell's environment to more homeostatic conditions are paramount to survival.
Quiescence is the counterpart to proliferation and is a normal part of the cell cycle. The cell's replicative cycle involves a myriad of molecular events that occur during the quiescent state (G0) and trigger the progression to the prereplicative (G1) phase. Cosenza S C, Owen T A, Soprano D R, Soprano K J, Evidence That the Time of Entry into S is Determined by Events Occurring in Early G1. J Biological Chem. 263; 12751-12758; 1988. The G0 phase represents not just the absence of signals for mitosis but an active repression of the genes needed for mitosis. This is an important distinction since cancer cells cannot enter G0 and as a consequence become immortal.
During quiescence, a cell will reduce in size yet remain dynamic and metabolically active. A quiescent cell is more notable for what it doesn't do such as synthesize DNA. Coller H A, Sang L, Roberts J M, A New Description of Cellular Quiescence. PLos Biology 4:0329-0349 2006. Quiescent cells are in a “state-of-readiness,” like hibernation, waiting for the appropriate signal that it is once more time to move to the G1 phase. Cells have a built-in conservation mechanism allowing it to survive for extended periods. Gray J V, Petsko G A, Johnston C, Ringe D, Singer R A, Werner-Washburne M, “Sleeping Beauty”: in Saccharomyces cerevisiae, Microbiology and Molecular Biology Reviews 68:2; 187-206, 2004. If the cell remains in the quiescence state for an extended period, however, its ability to proliferate diminishes. Stated differently, the longer a cell stays in abnormal quiescence the more likely it becomes that the cell will die via necrosis. Just as with early stage necrosis, however, early quiescence is a reversible event that can be corrected by changing the cell's environment and reduction of free radicals in the cell's environment appears to be critical to the reversal process. See, e.g., Coller H A, Sang L, Roberts J M, A New Description of Cellular Quiescence PLoS Biol 4(3):e83.doi:10.1371/journal.pbio.0040083 (2006).